Addition materials for improving plating speeds



United States Patent ADDITION MATERIALS FOR IMPROVING PLATING SPEEDS Edward B. Saubestre, Elmhurst, and Edward P. Bulan, Flushing, N.Y., assiguors, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware No Drawing. Application March 6, 1956 Serial No. 569,679

3 Claims. (Cl. 204-43) The present invention relates to plating methods, and in particular to improved alkaline-type plating solutions and processes for plating a variety of metals, including, without limitation, cadmium, copper, gold, silver and a solderable zinc-tin alloy.

Aqueous electrolytic plating solutions may be broadly divided into two types, namely acid-type and alkalinetype solutions. Acid-type solutions or baths are usually capable of operating at comparatively high plating speeds, but frequently produce nodular deposits when operated under normal processing conditions. Alkaline-type baths are superior to acid-type baths, particularly in producing fine-grained, non-nodular deposits and possessing superior throwing power. Accordingly, in an alkaline-type plating installation precautions are not required to assure anniform deposit; and the superior throwing power assures plating in regions which do not directly face the anode. However, the plating speed of alkaline-type electrolytes falls somewhat short of optimum requirements, particularly when compared to the high-speed plating which may be achieved with acid-type solutions.

It is an object of the present invention to provide improved plating methods and baths for increasing the plating speed of alkaline-type electrolytes. Specifically, it is within the contemplation of the present invention to provide addition materials for direct incorporation into conventional alkaline-type plating baths for increasing plating speed, without adversely affecting other desirable properties of such baths. 1

The speed of plating, that is the thickness of the plating deposited during a given period of time, is determined by the current density and current efliciency-of an installation. In that the plating speed is directly proportional to the product of current density and current efliciency, it is possible for the plater, having a choice of working over a given range of operating current densities, to select optimum operating conditions for plating.

From the foregoing it will be appreciated that wincrease the plating speed, it is necessary to increase the upper range of operating current density without a proportional loss of current eificiency; stated somewhat differently, the current value at which burning and dis-. coloring of the plating occurs limits the maximum plating speed for a given bath.

Accordingly, it is a further object of the present invention to produce improved alkaline-type plating baths 60- ing current densities whereby optimum conditions .of 65,

properties or qualities of the metal platings derived from said baths.

We have found that the plating speeds of alkaline-type plating baths may be increased by the addition to said bathsof at least two constituents selected from the group consisting of ammonium molybdate, gelatin and glycerin. Baths formulated according to the present invention .exhibit broad ranges of operating current densities, with comparatively high upper current density limits and ma sonably high efiiciency over the operating current range. Although current efficiency decreases vwith increasing values of current densities, such decrease, as a practical matter, does not diminish the plating speed in that the plating speed is directly proportional to the current density. For example, the plating speed will double for operation at twice a given current density, although the actual plating thickness may not quite come up to the theoretical value due to the decrease in current efficiency.

Advantageously, plating speeds may be improved in accordance with the present invention for alkaline-type plating baths containing cyanide ion and hydroxide ion which are used in the electrodeposition of cadmium, copper, gold, silver, and solderable zinc-tin alloy as described in detail in copending applicationSen'al No.

526,860, filed August 8, 1955 in the name of Edward B."

5 type plating solutions are as follows: 1 to 3 ounces per gallon of ammonium molybdate and /8 to $6 ounce per gallon of gelatin; or l to 3 ouncesper gallon of glycerin and A to A2 ounce per gallon of gelatin; or 1 to 3 ounces per gallon ammonium molybdate and 1 to 2 ounces per gallon glycerin. p

The preferred concentration of ammonium molybdate and gelatin was added to a solderable high zinc-low tin alloy bath prepared in accordance with the teachings of the aforementioned copending application. The bath formulation was as follows: 1

W V Example 1 f 2 oz./gal. ammonium molybdate% oz./gal. gelatin 13.3 oz./gal. K,SnO .3H 0 2.5 oz./ gal. ZnO 6.3 oz./gal.- KCN 4.6pz./gal. KOH Temperature, C.

The current efficiencies for that bath formulation of 5 Example lwith the stated addition agents in the range of to 225 amperes per square foot were as follows: 1

Current efficiency (percen 55 Current density (a.s.f.)

Example 2 3 oz./ gal. glycerin- /2 oz./ gal. gelatin in: 13.3 oz./gal. K SnO .3H O

2.5 oz./gal. ZnO

6.3 oz./gal. KCN

4.6 oz./ gal. KOH

Temperature, 65 C.

The current efliciencies for the plating bath of Example 2, in the operating range of'current denslties between 100 to 225 amperes per square foot, are as follows:

Current efliclency (percent) 64 60 55 50 45 41 Current density (a.s.f.) 100 125 150 175 200 225 The preferred concentration of ammonium molybdate and glycerin was added to the solderahle zinc-tin plating bath in accordance with Examples 1 and 2 and the current efliciencies obtained in the range of 100-225 amperes per square foot were the same as those obtained for Example 2.

Increased plating speeds are attainable with other types of alkaline baths, the formulations of which are to be found in various plating manuals and handbooks, such as the Electroplating Engineering Handbook by A. K. Graham, published by Reinhold Pub. Co. (1955). The properties of the followingbaths, each of which included as an addition agent two ounces per gallon of ammonium molybdate and A ounce per gallon of gelatin were investigated with the well known Hull cell operating at a current of 3 amperes. ,A typical cyanide-hydroxide formulation for electrodeposition of cadmium is as follows:

Example 3 A typicalcyanide hydroxide plating bath for the electrodeposition of copper is as follows:

Example 4 Copper cyanide oz./gal 8 Potassium cyanide do 12.5 Potassium carbonate do 2 Potassium hydroxide do.. 5.6 Temperature F 170 Results: Increase in the plating speed with the addition agent brought about by higher current efiiciency.

A typical formulation for gold plating is as follows:

Example Gold *(as cyanide) troy oz./gal 1 Potassium cyanide oz./gal 1.4 Temperature F 150 Results: No burning of the plating up to an upper operating range of current density of approximately 175 amperes per square foot. Plating was semi-bright to bright in the range of high current densities. In the absence of the addition agent the plating burned at current densities in excess of amperes per square foot.

A typical formulation for silver plating is as follows:

Example 6 Silver cyanide oz./gal 14 Potassium cyanide do 15 Potassium carbonate do-. 2 Potassium hydroxide do 4 Results: Slight increase in useable current density before burning occurs.

Temperature A typical formulation for zinc plating is as follows:

Example 7 Zinc oxide oz./gal 6 Sodium cyanide do.. 13 Sodium hydroxide do 6 Temperature F Results: Some decrease in burning at high current density,

but with markedly less plating at lower current densities.

The foregoing results appear to indicate that the addition agents are exceptionally effective for higher ratios.

copper, an intermediate high value for gold, 2.7 for silver, and 13.4 for zinc.

Although the addition agents in accordance with the pnesent invention are useful in increasing plating speeds for all types of Work processed in alkaline-cyanide plating baths,'a particularly important field of application is in wire and strip plating applications. As a typical example of one wire plating application, a molybdenum wire having a diameter of .0035 inch was plated with 6% gold. Operating 'with a bath of the formulation according to Example 5 and using the ammonium molybdate-gelatin additive, operation was successful at current densities up to 750 amperes per square foot without appreciable change in the deposit appearance. This upper limit of operating current density and higher plating speed is far in excess of the permissible current densities for baths according to Example 5, which have been heretofore operated at current densities under amperes per square foot.

What we claim is:

l. A process for plating of metals from an alkaline plating bath including cyanide ion and hydroxide ion, which comprises increasing the speed of operation of said'bath by adding to said bath an addition agent, said addition agent consisting of ammonium molybdate in a concentration of one to three ounces per gallon of said bath and at least one ingredient selected from the group consisting of gelatine in the range of from one-eighth to one-half ounce per gallon of bath and glycerine in the range of from one to two ounces per gallon of bath and passing current through said bath at a current density in'the rangefrom 80 to 225 amperes per square foot of cathode. I

2. In the jelect rodeposition of metals onto a cathodic workpiece from alkaline plating baths including cyanide ion and hydroxide ion, the steps including establishing a ratio of cyanideion to hydroxide ion in excess of 2.7, addingto said bath an addition agent for improving the plating speed of said bath, said addition agent consisting of ammonium molybdate in the range of from 1 to 3 ounces per gallon ofbath and gelatine in the range of from A; to /2 ounce per gallon of bath and electroion and hydroxide ion, the steps including establishing a ratio of cyanide ion to hydroxide ion in excess of 2.7, adding to said bath an addition agent for improving the plating speed of said bath, said addition agent consisting of ammonium molybdate in a concentration of from one to three ounces per gallon of bath and at least one ingredient selected from the group consisting of gelatine in the range of from one-eighth to one-half ounce per gallon of bath and glycerine in the range of from one to two ounces per gallon of bath and electrodepositing metal from said bath onto said cathodic workpiece at a current density in excess of 80 amperes per square foot of area of said cathodic workpiece.

References Cited in the file of this patent UNITED STATES PATENTS Darrah Mar. 17, 1914 Battle Oct. 24, 1916 Westbrook May 18, 1937 FOREIGN PATENTS Great Britain Nov. 28, 1939 

1. A PROCESS FOR PLATING OF METALS FROM AN ALKALINE PLATING BATH INCLUDING CYANIDE ION AND HYDROXIDE ION, WHICH COMPRISES INCREASING THE SPEED OF OPERATION OF SAID BATH BY ADDING TO SAID BATH AN ADDITION AGENT, SAID ADDITION AGENT CONSISTING OF AMMONIUM MOLYBDATE IN A CONCENTRATION OF ONE TO THREE OUNCES PER GALLON OF SAID BATH AND AT LEAST ONE INGREDIENT SELECTED FROM THE GROUP CONSISTING OF GELATINE IN THE RANGE OF FROM ONE-EIGHTH TO ONE-HALF OUNCE PER GALLON OF BATH AND GLYCERINE IN THE RANGE OF FROM ONE TO TWO OUNCES PER GALLON OF BATH AND PASSING CURRENT THROUGH SAID BATH AT A CURRENT DENSITY IN THE RANGE FROM 80 TO 225 AMPERES PER SQUARE FOOT OF CATHODE. 